JP2008288214A - Lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery with a high capacity capable of improving battery characteristics such as cycle characteristics. <P>SOLUTION: The battery has a spirally-wound electrode body 20 wherein a positive electrode 21 and negative electrode 22 are spirally wound via a separator 23. The negative electrode 11 includes at least one kind of a group of a simple substance, an alloy, a compound of a metal element or a semimetal element capable of forming lithium and an alloy. An electrolytic solution wherein electrolyte salt is dissolved in a solvent is impregnated in the separator 23. For the electrolyte salt, a light metal salt having a B-O bond or P-O bond such as difluoro (oxalato-O, O') lithium borate and tetra fluoro (oxalato-O, O') lithium phosphate can be used. By forming a stable coating, decomposition reaction of the solvent can be restrained, and reaction between the negative electrode 22 and the solvent can be prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery including an electrolyte together with a positive electrode and a negative electrode.

  In recent years, mobile electronic devices such as mobile phones, PDAs (Personal Digital Assistants) or notebook computers have been energetically reduced in size and weight, and as part of these efforts, Improvement of the energy density of a battery as a driving power source, particularly a secondary battery is strongly desired.

As a secondary battery capable of obtaining a high energy density, a battery using a lithium alloy as a negative electrode has been developed (see, for example, Patent Documents 1 and 2).
JP-A-6-325765 JP-A-7-230800

  However, when the charge and discharge are repeated, the lithium alloy has a problem of being pulverized and refined due to severe expansion and contraction. Therefore, when this is used for the negative electrode, the electron conductivity is reduced due to the fineness due to particle cracking or the reduction of the contact area between the particles in the negative electrode, or the decomposition reaction of the solvent is promoted due to the increase in the surface area, There was a problem that the cycle characteristics were not sufficient.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a lithium ion secondary battery having a high capacity and capable of improving battery characteristics such as cycle characteristics.

A lithium ion secondary battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The active material layer is composed of a simple substance of silicon, an alloy of silicon, a simple substance of tin, an alloy of tin, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ as a negative electrode active material, _{CoSi 2, NiSi 2, CaSi 2} , CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, It contains at least one member selected from the group consisting of SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO and LiSnO, and the electrolyte is difluoro [oxolato-O, O ′]. Ho Lithium acid, tetrafluoro [oxolato-O, O '] lithium phosphate, bis [oxolato-O, O'] lithium borate, difluorodi [oxolato-O, O '] lithium phosphate and tris [oxolato-O, O '] It contains any one lithium salt of lithium phosphate.

  According to the lithium ion secondary battery of the present invention, the negative electrode includes at least one selected from the group consisting of the simple substance, alloy, and compound of silicon described above as the negative electrode active material, and the simple substance, alloy, and compound of tin, and the electrolyte Difluoro [oxolato-O, O ′] lithium borate, tetrafluoro [oxolato-O, O ′] lithium phosphate, bis [oxolato-O, O ′] lithium borate, difluorodi [oxolato-O, O ′] phosphorus Since any one lithium salt of lithium acid and tris [oxolato-O, O ′] lithium phosphate is included, the decomposition reaction of the electrolyte can be suppressed. In addition, the reaction between the negative electrode and the electrolyte can be prevented. Therefore, a high capacity can be obtained, charge / discharge efficiency can be improved, and various characteristics such as cycle characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces and a positive electrode active material layer 21B provided on both surfaces or one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 21B includes, for example, a positive electrode material capable of inserting and extracting lithium as a positive electrode active material.

The positive electrode material capable of inserting and extracting lithium preferably contains a lithium-containing compound containing lithium, a transition metal element, and oxygen in order to increase the energy density. It is more preferable if it contains at least one member selected from the group consisting of cobalt (Co), nickel and manganese (Mn). Examples of such a lithium-containing compound include LiCoO _{2 and} LiNiCoO ₂ .

  Such a positive electrode material is prepared by, for example, mixing lithium carbonate, nitrate, oxide or hydroxide with transition metal carbonate, nitrate, oxide or hydroxide so as to have a desired composition. And then pulverized and then fired at a temperature in the range of 600 ° C. to 1000 ° C. in an oxygen atmosphere.

  The positive electrode active material layer 21B also contains, for example, a conductive agent, and may further contain a binder as necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one or more of them are used in combination. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Examples of the binder include synthetic rubbers such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used. For example, when the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use a styrene butadiene rubber or a fluorine rubber having high flexibility as the binder.

  The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposed surfaces, and a negative electrode active material layer 22B provided on both surfaces or one surface of the negative electrode current collector 22A. The anode current collector 22A is preferably made of, for example, copper (Cu), stainless steel, nickel, titanium (Ti), tungsten (W), molybdenum (Mo), aluminum, or the like. Among these, the anode active material layer 22B and In some cases, it is more preferable to use a metal that easily causes alloying. For example, as will be described later, when the negative electrode active material layer 22B includes at least one member selected from the group consisting of a simple substance, an alloy, and a compound of silicon (Si) or tin (Sn), copper, titanium, aluminum, nickel, etc. May be mentioned as a material that is easily alloyed. The negative electrode current collector 22A may be composed of a single layer, but may be composed of a plurality of layers. In that case, the layer in contact with the negative electrode active material layer 22B may be made of a metal material that is easily alloyed with the negative electrode active material layer 22B, and the other layers may be made of another metal material.

  The surface roughness of the negative electrode current collector 22A is determined when the negative electrode active material layer 22B is formed by a vapor phase method, a liquid phase method, a sintering method, or a combination thereof, as described later, or the negative electrode active material layer In the case of alloying at least part of the interface with 22B, the arithmetic average roughness Ra is preferably 0.1 μm or more. This is because the shape of cracks generated by the expansion and contraction of the negative electrode active material layer 22 with charge / discharge can be controlled, and the stress can be dispersed to suppress the structural breakdown of the negative electrode 22.

  The negative electrode active material layer 22B includes, for example, a group consisting of a simple substance, an alloy and a compound of a metal element capable of forming an alloy with lithium and a simple substance, an alloy and a compound of a metalloid capable of forming an alloy with lithium as the negative electrode active material. Of at least one of them. Thus, the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium by the negative electrode active material, and a high energy density can be obtained.

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), and cadmium. (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). It is done. Examples of these compounds include those represented by the chemical formula Mα _s1 Mβ _s2 Li _s3 or the chemical formula Mα _s4 Mγ _s5 Mδ _s6 . In these chemical formulas, Mα represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mβ represents at least one of a metal element and a metalloid element other than lithium and Mα, Mγ represents at least one of nonmetallic elements, and Mδ represents at least one of metallic elements and metalloid elements other than Mα. The values of s1, s2, s3, s4, s5, and s6 are s1> 0, s2 ≧ 0, s3 ≧ 0, s4> 0, s5> 0, and s6 ≧ 0, respectively.

  Among these, a simple substance, an alloy or a compound of a group 4B metal element or semimetal element in the short periodic table is preferable, and a simple substance of silicon or tin, or an alloy or compound thereof is particularly preferable. This is because the simple substance, alloy, and compound of silicon or tin have a large ability to occlude and release lithium, and depending on the combination, the energy density of the anode 22 can be made higher than that of conventional graphite. These may be crystalline or amorphous.

Specific examples of such compounds include LiAl, AlSb, CuMgSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , and CaSi. _{2, CrSi 2, Cu 5 Si} , FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO.

  The anode active material layer 22B is preferably formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method. Breakage due to expansion / contraction of the negative electrode active material layer 22B due to charge / discharge can be suppressed, and the negative electrode current collector 22A and the negative electrode active material layer 22B can be integrated, and electrons in the negative electrode active material layer 22B can be integrated. This is because the conductivity can be improved. In addition, the binder and voids can be reduced or eliminated, and the negative electrode 22 can be made thin.

  The negative electrode active material layer 22B is preferably alloyed with the negative electrode current collector 22A at least at a part of the interface with the negative electrode current collector 22A. Specifically, it is preferable that the constituent element of the negative electrode current collector 22A is diffused in the negative electrode active material layer 22B, the constituent element of the negative electrode active material is diffused in the negative electrode current collector 22A, or they are mutually diffused at the interface. This alloying often occurs at the same time when the anode active material layer 22B is formed by a vapor phase method, a liquid phase method or a sintering method, but is caused by further heat treatment or during initial charging. But you can.

  The negative electrode active material layer 22B may also be formed by coating, specifically, a negative electrode active material powder and, if necessary, a binder such as polyvinylidene fluoride. In this case, in addition to at least one member selected from the group consisting of simple elements, alloys and compounds of metal elements or metalloid elements capable of forming an alloy with lithium, other negative electrode active materials may be included. Other negative electrode active materials are preferably carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. Since these carbon materials undergo very little change in crystal structure during charge and discharge, they should be included in addition to simple elements, alloys or compounds of metal elements or metalloid elements capable of forming an alloy with lithium. This is because a high energy density can be obtained and excellent cycle characteristics can be obtained.

As the graphite, for example, the true density is preferably 2.10 g / cm ³ or more, and more preferably 2.18 g / cm ³ or more. In order to obtain such a true density, it is necessary that the (002) plane C-axis crystallite thickness is 14.0 nm or more. Further, the (002) plane spacing is preferably less than 0.340 nm, and more preferably in the range of 0.335 nm to 0.337 nm.

The graphite may be natural graphite or artificial graphite. If it is artificial graphite, for example, it can be obtained by carbonizing an organic material, subjecting it to high-temperature heat treatment, and pulverizing and classifying it. In the high temperature heat treatment, for example, carbonization is performed at 300 ° C. to 700 ° C. in an inert gas stream such as nitrogen (N ₂ ) as necessary, and the temperature is increased to 900 ° C. to 1500 ° C. at a rate of 1 ° C. to 100 ° C. per minute. This temperature is maintained for about 0 to 30 hours and calcined, and heated to 2000 ° C. or higher, preferably 2500 ° C. or higher, and this temperature is maintained for an appropriate time.

  As the organic material to be a starting material, coal or pitch can be used. For pitch, for example, tars obtained by thermally decomposing coal tar, ethylene bottom oil or crude oil at high temperature, asphalt, etc. (vacuum distillation, atmospheric distillation or steam distillation), thermal polycondensation, extraction, There are those obtained by chemical polycondensation, those produced when wood is refluxed, polyvinyl chloride resins, polyvinyl acetate, polyvinyl butyrate or 3,5-dimethylphenol resins. These coals or pitches exist as liquids at a maximum temperature of about 400 ° C. during carbonization, and the aromatic rings are condensed and polycyclic by being held at that temperature, and are in a stacked orientation state. It becomes a solid carbon precursor, that is, semi-coke (liquid phase carbonization process).

  Examples of organic materials include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, or derivatives thereof (for example, carboxylic acids, carboxylic anhydrides, and carboxylic acids of the above-described compounds). Imide), or mixtures thereof. Furthermore, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine, or a derivative thereof, or a mixture thereof can also be used.

  The pulverization may be performed either before or after carbonization, calcination, or during the temperature raising process before graphitization. In these cases, heat treatment for graphitization is finally performed in a powder state. However, in order to obtain a graphite powder having a high bulk density and high fracture strength, it is preferable to form a raw material and then perform a heat treatment, and pulverize and classify the obtained graphitized molded body.

  For example, when producing a graphitized molded body, coke as a filler and a binder pitch as a molding agent or a sintering agent are mixed and molded, and then the molded body is heat-treated at a low temperature of 1000 ° C. or lower. After repeating the firing step and the pitch impregnation step of impregnating the binder pitch melted in the fired body several times, heat treatment is performed at a high temperature. The impregnated binder pitch is carbonized and graphitized in the above heat treatment process. Incidentally, in this case, since filler (coke) and binder pitch are used as raw materials, it is graphitized as a polycrystal, and sulfur and nitrogen contained in the raw materials are generated as a gas during heat treatment. A minute hole is formed in the path. Therefore, this vacancy makes it easy for the lithium occlusion / release reaction to proceed, and there is also an advantage that the treatment efficiency is industrially high. In addition, as a raw material of a molded object, you may use the filler which has a moldability and sintering property in itself. In this case, it is not necessary to use a binder pitch.

As non-graphitizable carbon, (002) plane spacing is 0.37 nm or more, true density is less than 1.70 g / cm ³ , and in differential thermal analysis (DTA) in air What does not show an exothermic peak at 700 ° C. or higher is preferable.

  Such non-graphitizable carbon can be obtained, for example, by heat-treating an organic material at about 1200 ° C., and pulverizing and classifying it. In the heat treatment, for example, carbonization is performed at 300 ° C. to 700 ° C. as necessary (solid-phase carbonization process), and then the temperature is raised to 900 ° C. to 1300 ° C. at a rate of 1 ° C. to 100 ° C. per minute. It is performed by holding for about 30 hours. The pulverization may be performed before or after carbonization or during the temperature raising process.

  As the organic material to be the starting material, for example, furfuryl alcohol or furfural polymer, copolymer, or furan resin that is a copolymer of these polymers and other resins can be used. Crustaceans including phenolic resins, acrylic resins, vinyl halide resins, polyimide resins, polyamideimide resins, polyamide resins, conjugated resins such as polyacetylene or polyparaphenylene, cellulose or derivatives thereof, coffee beans, bamboos, and chitosan Also, biocellulose using bacteria can be used. Further, a compound in which a functional group containing oxygen is introduced (so-called oxygen cross-linking) into petroleum pitch in which the atomic ratio H / C between the hydrogen atom (H) and the carbon atom (C) is 0.6 to 0.8, for example. Can also be used.

  The oxygen content in this compound is preferably 3% or more, and more preferably 5% or more (see Japanese Patent Application Laid-Open No. 3-252053). This is because the oxygen content affects the crystal structure of the carbon material, and the physical properties of the non-graphitizable carbon can be increased and the capacity of the anode 22 can be improved at a content higher than this. Incidentally, petroleum pitch, for example, tar (as obtained from pyrolysis of coal tar, ethylene bottom oil or crude oil, etc.) or asphalt is distilled (vacuum distillation, atmospheric distillation or steam distillation), It can be obtained by condensation, extraction or chemical polycondensation. Examples of the method for forming an oxidative bridge include a wet method in which an aqueous solution such as nitric acid, sulfuric acid, hypochlorous acid, or a mixed acid thereof is reacted with petroleum pitch, or an oxidizing gas such as air or oxygen is reacted with petroleum pitch. Or a dry method in which a solid reagent such as sulfur, ammonium nitrate, ammonia persulfate, or ferric chloride is reacted with petroleum pitch.

  Note that the organic material that is a starting material is not limited to these, and any other organic material may be used as long as it is an organic material that can be converted into non-graphitizable carbon through a solid-phase carbonization process by oxygen crosslinking treatment or the like.

  As the non-graphitizable carbon, in addition to those produced using the above-mentioned organic materials as starting materials, compounds described in JP-A-3-137010 are mainly composed of phosphorus, oxygen and carbon. It is preferable because it shows physical property parameters.

  The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable because a shutdown effect can be obtained in the range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains a liquid solvent, for example, a nonaqueous solvent such as an organic solvent, and an electrolyte salt dissolved in the nonaqueous solvent, and may contain various additives as necessary. The liquid non-aqueous solvent is made of, for example, a non-aqueous compound and has an intrinsic viscosity at 25 ° C. of 10.0 mPa · s or less. In addition, the intrinsic viscosity in a state where the electrolyte salt is dissolved may be 10.0 mPa · s or less. When a solvent is formed by mixing a plurality of types of nonaqueous compounds, the intrinsic viscosity in the mixed state is What is necessary is just 10.0 mPa * s or less.

  As such a nonaqueous solvent, various conventionally used nonaqueous solvents can be used. Specifically, cyclic carbonates such as propylene carbonate or ethylene carbonate, chain esters such as diethyl carbonate, dimethyl carbonate or ethylmethyl carbonate, or ethers such as γ-butyrolactone, sulfolane, 2-methyltetrahydrofuran or dimethoxyethane Is mentioned. These may be used alone or in combination of two or more. In particular, from the viewpoint of oxidation stability, it is preferable to include a carbonate ester.

  As an electrolyte salt, a light metal having an M—X bond (where M represents a transition metal element or a group 3B element, a group 4B element or a group 5B element in the short-period periodic table, and X represents oxygen or sulfur). It is preferable to contain any one kind or two or more kinds of salts. Such a light metal salt is considered to form a stable film on the surface of the negative electrode 22, suppress the decomposition reaction of the solvent in the negative electrode 22, and prevent the reaction between the negative electrode 22 and the solvent. Because.

  Of these, cyclic compounds are preferred. This is because the cyclic portion is also considered to be involved in the formation of the film, and a stable film can be obtained.

  Examples of such light metal salts include compounds represented by Chemical Formula 1.

式中、Ｒ１１は化２または化３に示した基を表し、Ｒ１２はハロゲン，アルキル基，ハロゲン化アルキル基，アリール基またはハロゲン化アリール基を表し、Ｘ１１およびＸ１２は酸素または硫黄をそれぞれ表し、Ｍ１１は遷移金属元素または短周期型周期表における３Ｂ族元素，４Ｂ族元素あるいは５Ｂ族元素を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウムを表し、ａは１〜４の整数であり、ｂは０〜８の整数であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。

In the formula, R11 represents a group shown in Chemical Formula 2 or Chemical Formula 3, R12 represents a halogen, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, X11 and X12 each represent oxygen or sulfur, M11 represents a transition metal element or a 3B group element, a 4B group element or a 5B group element in the short periodic table, M21 represents a 1A group element, a 2A group element or aluminum in the short periodic table, and a is 1 to 1 It is an integer of 4, b is an integer of 0-8, c, d, e, and f are integers of 1-3, respectively.

Ｒ２１は、アルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。

R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group.

  Specifically, a compound represented by Chemical formula 4 can be given.

式中、Ｒ１１は化５または化６に示した基を表し、Ｒ１２はハロゲン，アルキル基，ハロゲン化アルキル基，アリール基またはハロゲン化アリール基を表し、Ｘ１１およびＸ１２は酸素または硫黄をそれぞれ表し、Ｍ１１は遷移金属元素または短周期型周期表における３Ｂ族元素，４Ｂ族元素あるいは５Ｂ族元素を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウムを表し、ｂ１は１〜８の整数であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。

In the formula, R11 represents a group shown in Chemical Formula 5 or Chemical Formula 6, R12 represents a halogen, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, X11 and X12 each represents oxygen or sulfur, M11 represents a transition metal element or a group 3B element, a group 4B element or a group 5B element in the short period type periodic table, M21 represents a group 1A element, a group 2A element or aluminum in the short period type periodic table; It is an integer of 8, and c, d, e and f are integers of 1 to 3, respectively.

Ｒ２１は、アルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。

R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group.

  Among these, a compound represented by Chemical formula 7 is preferable.

式中、Ｒ１１は化８または化９に示した基を表し、Ｒ１３はハロゲンを表し、Ｍ１２はリン（Ｐ）またはホウ素（Ｂ）を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウムを表し、ｂ２は２または４であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。

In the formula, R11 represents a group shown in Chemical formula 8 or Chemical formula 9, R13 represents halogen, M12 represents phosphorus (P) or boron (B), M21 represents a group 1A element or 2A in the short-period type periodic table Represents a group element or aluminum, b2 is 2 or 4, and c, d, e, and f are integers of 1 to 3, respectively.

Ｒ２１は、アルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。

R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group.

  More specifically, difluoro [oxolato-O, O ′] lithium borate represented by the chemical formula 10 or tetrafluoro [oxolato-O, O ′] lithium phosphate represented by the chemical formula 11 is more preferable. . A higher effect can be obtained when a B—O bond or a P—O bond is provided, and a higher effect is obtained particularly when an O—B—O bond or an O—P—O bond is provided. Because it can.

  Further, bis [oxolato-O, O ′] lithium borate represented by Chemical formula 12, difluorodi [oxolato-O, O ′] lithium phosphate represented by Chemical formula 13, or tris [oxolatato represented by Chemical formula 14 -O, O '] lithium phosphate is also preferred. These are those in which a in Chemical Formula 1 is 2 or 3, but, as in Chemical Formulas 10 and 11, have an O—B—O bond or an O—P—O bond, and can obtain a high effect. Because.

  In addition to this, as the lithium salt having an MX bond, lithium bis [1,2-benzenediolato (2-)-O, O ′] lithium borate represented by Chemical formula 15 or Chemical formula 16 The tris [1,2-benzenediolato (2-)-O, O ′] lithium phosphate represented is also preferably exemplified for the same reason as described above.

In addition to the light metal salt having an MX bond, the electrolyte salt preferably contains any one or more of other light metal salts in combination. This is because internal resistance can be reduced and battery characteristics such as heavy load characteristics can be improved. Examples of other light metal salts include LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBr, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) or other lithium salt represented by Chemical Formula 17 or LiC (CF ₃ SO ₂ ) _{3 and the} like, and lithium salts represented by the formula 18 are mentioned.

式中、ｍおよびｎは１以上の整数である。

In the formula, m and n are integers of 1 or more.

式中、ｐ，ｑおよびｒは１以上の整数である。

In the formula, p, q and r are integers of 1 or more.

Among these, if at least one of the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , lithium salt represented by Chemical Formula 17 and lithium salt represented by Chemical Formula 18 is included, It is preferable because a higher effect can be obtained and a high conductivity can be obtained, and it is particularly preferable to include LiPF ₆ .

  The content (concentration) of the electrolyte salt is preferably in the range of 0.3 mol / kg to 3.0 mol / kg with respect to the solvent. Outside this range, there is a risk that sufficient battery characteristics may not be obtained due to an extreme decrease in ionic conductivity. Among them, the content of the light metal salt having an M—X bond is preferably in the range of 0.01 mol / kg to 2.0 mol / kg with respect to the solvent. This is because a higher effect can be obtained within this range.

  Instead of the electrolytic solution, a gel electrolyte in which an electrolytic solution is held in a polymer compound may be used. The gel electrolyte is not particularly limited as long as the ion conductivity is 1 mS / cm or more at room temperature, and the composition and the structure of the polymer compound are not particularly limited. The electrolyte solution (that is, liquid solvent, electrolyte salt, and additive) is as described above. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, poly Examples thereof include siloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use a polymer compound having a polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene or polyethylene oxide structure. The amount of the polymer compound added to the electrolytic solution varies depending on the compatibility between the two, but it is usually preferable to add a polymer compound corresponding to 3% by mass to 50% by mass of the electrolytic solution.

  The content of the electrolyte salt is the same as that in the case of the electrolytic solution. However, the term “solvent” here means not only a liquid solvent but also a concept that can dissociate the electrolyte salt and has a wide range of ionic conductivity. Therefore, when using what has ion conductivity for a high molecular compound, the high molecular compound is also contained in a solvent.

  For example, the secondary battery can be manufactured as follows.

  First, for example, the positive electrode active material layer 21B is formed on the positive electrode current collector 21A to produce the positive electrode 21. The positive electrode active material layer 21B is prepared, for example, by mixing a positive electrode active material powder, a conductive agent, and a binder to prepare a positive electrode mixture, and then using the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone. The positive electrode mixture slurry is dispersed to form a positive electrode mixture slurry, and the positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression molded.

  Further, for example, the negative electrode active material layer 22B is formed on the negative electrode current collector 22A to produce the negative electrode 22. The negative electrode active material layer 22B is formed, for example, by depositing a negative electrode active material on the negative electrode current collector 22A by a vapor phase method or a liquid phase method. Further, a precursor layer containing a particulate negative electrode active material may be formed on the negative electrode current collector 22A, and then formed by a sintering method in which the precursor layer is sintered. Alternatively, a vapor phase method, a liquid phase method, and a sintering method may be used. A combination of two or three of the methods may be used. Thus, by forming the negative electrode active material layer 22B by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, in some cases, at least at the interface with the negative electrode current collector 22A Part of the negative electrode active material layer 22B alloyed with the negative electrode current collector 22A is formed.

  Note that in order to further alloy the interface between the negative electrode current collector 22A and the negative electrode active material layer 22B, heat treatment may be further performed in a vacuum atmosphere or a non-oxidizing atmosphere. In particular, when the negative electrode active material layer 22B is formed by plating described later, the negative electrode active material layer 22B may be difficult to be alloyed even at the interface with the negative electrode current collector 22A. Therefore, this heat treatment may be performed as necessary. preferable. In addition, even in the case of forming by the vapor phase method, the characteristics may be improved by alloying the interface between the negative electrode current collector 22A and the negative electrode active material layer 22B. It is preferable to perform a heat treatment.

  As the vapor phase method, for example, a physical deposition method or a chemical deposition method can be used. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a thermal CVD (Chemical Vapor Deposition) A chemical vapor deposition method) or a plasma CVD method can be used. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the sintering method, a known method can be used, for example, an atmosphere sintering method, a reaction sintering method, or a hot press sintering method can be used.

  Moreover, you may make it form the negative electrode active material layer 22B by application | coating. Specifically, for example, a negative electrode active material powder and a binder are mixed to prepare a negative electrode mixture, and then the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste. The negative electrode mixture slurry may be applied to the negative electrode current collector 22A, dried, and compression molded. However, the adhesion between the negative electrode current collector 22A and the negative electrode active material layer 22B is enhanced by forming by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method. In addition, as described above, the anode active material layer 22B is preferably formed at the same time as the alloying of the anode current collector 22A and the anode active material layer 22B often proceeds.

  Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, an electrolyte is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte. On the other hand, when discharging is performed, for example, lithium ions are separated from the negative electrode 22 and inserted into the positive electrode 21 through the electrolyte. At that time, a stable coating is formed on the surface of the negative electrode 22 by the light metal salt having an M—X bond, and the decomposition reaction of the solvent is suppressed. Further, the reaction between the negative electrode 22 and the solvent is prevented.

  As described above, in the present embodiment, since the electrolyte includes a light metal salt having an M—X bond, the negative electrode 22 is composed of a simple substance, an alloy, and a compound of a metal element or a metalloid element capable of forming an alloy with lithium. Even when at least one member of the group is contained, the decomposition reaction of the solvent in the negative electrode 22 can be suppressed. Further, the reaction between the negative electrode 22 and the solvent can be prevented. Therefore, a high capacity can be obtained, charge / discharge efficiency can be improved, and various characteristics such as cycle characteristics can be improved.

  In particular, if a light metal salt having a B—O bond or a P—O bond is included, it is higher if a light metal salt having an O—B—O bond or an O—P—O bond is included. An effect can be obtained.

Moreover, if other light metal salts are included in addition to the light metal salt having an MX bond, the internal resistance can be reduced, and battery characteristics such as heavy load characteristics can be improved. Furthermore, if LiPF ₆ is included in addition to the light metal salt having an MX bond, the electrical conductivity can be improved, and battery characteristics such as cycle characteristics can be improved.

  Further, specific embodiments of the present invention will be described in detail with reference to the drawings.

(Examples 1-1 to 1-18)
The cylindrical secondary battery shown in FIGS. 1 and 2 was produced. First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which was uniformly applied to both surfaces of the positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm. The positive electrode active material layer 21B was formed by drying and compression molding, and this was cut into a strip shape to produce a strip-like positive electrode 21. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

  Further, 20 g of silicon powder and 80 g of copper powder were mixed, and this mixture was put in a quartz boat, heated to 1000 ° C. in an argon gas atmosphere, and allowed to cool to room temperature. The lump thus obtained was pulverized by a ball mill in an argon gas atmosphere to obtain a copper-silicon (Cu—Si) alloy powder as a negative electrode active material. When the obtained copper-silicon alloy powder was observed with a scanning electron microscope, the average particle size was about 10 μm. 80 parts by mass of the copper-silicon alloy powder, 10 parts by mass of flaky graphite as a negative electrode active material and a conductive agent, 2 parts by mass of acetylene black, and 8 parts by mass of polyvinylidene fluoride as a binder are mixed together. An agent was prepared. Subsequently, the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, which was uniformly applied to both surfaces of a negative electrode current collector 22A made of a strip-shaped electrolytic copper foil having a thickness of 15 μm. The negative electrode active material layer 22B was formed by compression molding, and this was cut into strips to produce a strip-shaped negative electrode 22. After that, a nickel negative electrode lead 26 was attached to one end of the negative electrode current collector 22A.

  After preparing the positive electrode 21 and the negative electrode 22, a separator 23 made of a microporous polyethylene film having a thickness of 25 μm is prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 are stacked in this order to form a spiral structure. The wound electrode body 20 was produced by winding a number of times.

  After producing the wound electrode body 20, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The wound electrode body 20 was housed inside a nickel-plated iron battery can 11. After that, an electrolytic solution was injected into the battery can 11 by a reduced pressure method. As the electrolytic solution, a solution obtained by dissolving a light metal salt as an electrolyte salt in a solvent in which 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate were mixed was used.

  At that time, the kind and content of the light metal salt were changed as shown in Table 1 in Examples 1-1 to 1-18. Among them, Example 1-1 uses difluoro [oxolato-O, O ′] lithium borate represented by Chemical Formula 10, and Examples 1-2 to 1-16 are difluoro [oxolato- O, O ′] lithium borate and other light metal salts are used in combination. Example 1-17 is a tetrafluoro [oxolato-O, O ′] lithium phosphate represented by the formula 11 In Example 1-18, tetrafluoro [oxolato-O, O ′] lithium phosphate and another light metal salt were mixed and used.

  After injecting the electrolyte into the battery can 11, the battery lid 14 was caulked to the battery can 11 through the gasket 17 coated with asphalt on the surface, whereby Examples 1-1 to 1-18 had a diameter of 14 mm, A cylindrical secondary battery having a height of 65 mm was obtained.

Further, as Comparative Example 1-1 with respect to Examples 1-1 to 1-18, only LiPF ₆ was used as an electrolyte salt, and the content thereof was 1.0 mol / kg with respect to the solvent. Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-18.

  With respect to the fabricated secondary batteries of Examples 1-1 to 1-18 and Comparative Example 1-1, a charge / discharge test was performed to examine initial capacity, internal resistance, and cycle characteristics. Charging is performed until the battery voltage reaches 4.2 V at a constant current of 700 mA, and then until the current reaches 2 mA at a constant voltage of 4.2 V. The discharging is performed at a constant current of 700 mA and the battery voltage is 2.5 V. Went until it reached. The initial capacity is the discharge capacity of the first cycle obtained in this way. The internal resistance was determined by performing an AC impedance measurement at 1 kHz in the charge state at the first cycle. As the cycle characteristics, the capacity retention ratio at the 100th cycle relative to the initial capacity (capacity at the 100th cycle / initial capacity) × 100 was determined. The obtained results are shown in Table 1.

  As can be seen from Table 1, according to Examples 1-1 to 1-18 using a light metal salt having an M—X bond, the initial capacity and the capacity retention ratio were compared with those of Comparative Example 1-1 which was not used. The internal resistance could be further reduced. That is, when the anode active material layer 22B contains a compound of a metalloid element capable of forming an alloy with lithium, if the electrolyte contains a light metal salt having an MX bond, the capacity and cycle characteristics are improved. It has been found that the internal resistance can be reduced.

Further, as can be seen from Examples 1-1 to 1-8, 1-12 to 1-16 and Examples 1-17 and 1-18, a light metal salt having an MX bond and another light metal salt are mixed. According to Examples 1-2 to 1-8, 1-12 to 1-16 and Example 1-18, Example 1-1 and only light metal salt having an M—X bond were used. Compared with Example 1-17, the internal resistance could be reduced, and the effect was particularly great when LiPF ₆ was used. Furthermore, when the light metal salt having an M—X bond and another light metal salt were mixed and used, a higher capacity retention ratio could be obtained by adjusting the content thereof. That is, it was found that a higher effect can be obtained if the electrolytic solution contains a light metal salt having an MX bond and another light metal salt.

  In addition, if the content of the light metal salt having an MX bond is 0.01 mol / kg or more and 2.0 mol / kg or less, the capacity and cycle characteristics can be improved and the internal resistance can be reduced. Was confirmed.

(Examples 2-1 and 2-2)
Using tin as a negative electrode active material, a negative electrode active material layer 22B made of tin having a thickness of 2 μm is formed by electron beam evaporation on a negative electrode current collector 22A made of electrolytic copper foil and having a thickness of 25 μm, and heat-treated at 200 ° C. for 12 hours. A secondary battery was fabricated in the same manner as in Examples 1-1 to 1-18 except that the anode 22 was fabricated. At that time, the type and content of the light metal salt were changed as shown in Table 2. In addition, when the obtained negative electrode 22 was analyzed by XPS (X-ray Photoelectron Spectroscopy; X-ray photoelectron spectroscopy), AES (Auger Electron Spectroscopy; Auger electron spectroscopy), and X-ray diffraction method, the negative electrode active material layer 22B was found. It was confirmed that at least part of the interface with the negative electrode current collector 22A was alloyed with the negative electrode current collector 22A.

Further, as Comparative Example 2-1 with respect to Examples 2-1 and 2-2, except that only LiPF ₆ was used as the electrolyte salt, and the content thereof was 1.0 mol / kg with respect to the solvent, the others were Secondary batteries were fabricated in the same manner as in Examples 2-1 and 2-2.

  The fabricated secondary batteries of Examples 2-1 and 2-2 and Comparative Example 2-1 were charged and discharged in the same manner as in Examples 1-1 to 1-18, and the initial capacity, internal resistance, and cycle characteristics were Each was investigated. The results are shown in Table 2 together with the results of Examples 1-1 and 1-4 and Comparative example 1-1.

  As can be seen from Table 2, according to Examples 2-1 and 2-2 using a light metal salt having an M-X bond, as in Examples 1-1 and 1-4, Comparative Example 2 which was not used. Compared to -1, the initial capacity and capacity retention ratio could be increased, and the internal resistance could be further reduced. In particular, in Example 2-2, in which a light metal salt having an M—X bond and another light metal salt were mixed and used, the effect was great.

  That is, even when tin, which is a simple substance of a metal element capable of forming an alloy with lithium, is used as the negative electrode active material, or when the negative electrode active material layer 22B is formed by a vapor phase method, MX is added to the electrolyte solution. It has been found that if a light metal salt having a bond is included, the capacity and cycle characteristics can be improved, and the internal resistance can be reduced. It has also been found that higher effects can be obtained if the electrolyte contains a light metal salt having an MX bond and another light metal salt.

(Examples 3-1 to 3-35, Reference examples 3-36 to 3-39)
Silicon as the negative electrode active material was deposited to form a negative electrode active material layer, and the coin-type secondary battery shown in FIG. 3 was produced. In the secondary battery, a disk-shaped positive electrode 31 and a negative electrode 32 are stacked with a separator 33 interposed between them, and are housed between an outer can 34 and an outer cup 35.

  First, a lithium / cobalt composite oxide having an average particle diameter of 5 μm as a positive electrode active material, carbon black as a conductive agent, and polyvinylidene fluoride as a binder are combined with lithium / cobalt composite oxide: carbon black: polyfluoride. The positive electrode mixture was prepared by mixing at a mass ratio of vinylidene chloride = 92: 3: 5. Next, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is applied to a positive electrode current collector 31A made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression molded. Thus, the positive electrode active material layer 31B was formed, and the positive electrode 31 was produced.

  Further, an electrolytic copper foil having an arithmetic average roughness Ra of 0.5 μm and a thickness of 35 μm is prepared as the negative electrode current collector 32A, and a negative electrode active material layer 32B having a thickness of 4 μm made of silicon is deposited on the negative electrode current collector 32A by vapor deposition. After that, heat treatment was performed to form the negative electrode 32. When the obtained negative electrode 32 was analyzed by XPS and AES, it was confirmed that the negative electrode active material layer 32B was alloyed with the negative electrode current collector 32A in at least a part of the interface with the negative electrode current collector 32A.

  Next, a negative electrode 32 and a polypropylene separator 33 having a thickness of 25 μm are sequentially laminated in the center of the outer cup 35, and after injecting an electrolyte, the outer can 34 containing the positive electrode 31 is covered and caulked through a gasket 36. A coin-type secondary battery having a diameter of 20 mm and a height of 1.6 mm was produced. As the electrolytic solution, a solution obtained by dissolving a light metal salt as an electrolyte salt in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used. In that case, the kind and content of the light metal salt were changed as shown in Tables 3 to 6 in Examples 3-1 to 35-35 and Reference Examples 3-36 to 3-39.

  Among these, Example 3-1 uses difluoro [oxolato-O, O ′] lithium borate represented by Chemical Formula 10, and Examples 3-2 to 3-21 are difluoro [oxolato-O]. , O ′] lithium borate and other light metal salts are mixed and used. Example 3-22 uses bis [oxolato-O, O ′] lithium borate represented by the formula 12. Examples 3-23 to 3-29 are bis [oxolato-O, O, '] A mixture of lithium borate and other light metal salts. In Example 3-30, tetrafluoro [oxolato-O, O ′] lithium phosphate represented by Chemical Formula 11 was used, and in Example 3-31, tetrafluoro [oxolato-O, O ′] was used. It is a mixture of lithium phosphate and other light metal salts. Example 3-32 uses difluorodi [oxolato-O, O ′] lithium phosphate represented by Chemical formula 13, and Example 3-33 uses difluorodi [oxolato-O, O ′] phosphoric acid. This is a mixture of lithium and other light metal salts. Example 3-34 uses tris [oxolato-O, O ′] lithium phosphate represented by chemical formula 14, and Example 3-35 uses tris [oxolato-O, O ′] phosphoric acid. This is a mixture of lithium and other light metal salts. Reference Example 3-36 uses bis [1,2-benzenediolato (2-)-O, O ′] lithium borate represented by Chemical Formula 15, and Reference Example 3-37 [1,2-Benzenediolato (2-)-O, O ′] lithium borate and other light metal salts are used in combination. Reference Example 3-38 uses tris [1,2-benzenediolato (2-)-O, O ′] lithium phosphate represented by Chemical Formula 16, and Reference Example 3-39 [1,2-Benzenediolato (2-)-O, O ′] lithium phosphate and other light metal salts are used in combination.

Moreover, as Comparative Examples 3-1 to 3-6 with respect to Examples 3-1 to 35-35 and Reference Examples 3-36 to 3-39, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN ( Except that only one of CF ₃ SO ₂ ) _{2 and} LiC (CF ₃ SO ₂ ) ₃ was used and the content thereof was 1.0 mol / kg with respect to the solvent, the others were the same as in Example 3- 1-3-35, Rechargeable batteries were fabricated in the same manner as Reference Examples 3-36 to 3-39.

For the fabricated secondary batteries of Examples 3-1 to 35-35, Reference Examples 3-36 to 3-39 and Comparative Examples 3-1 to 3-6, a charge / discharge test was performed, and the initial capacity and cycle characteristics were Examined. Charging is performed at a constant current density of 1 mA / cm ² until the battery voltage reaches 4.2 V, and then at a constant voltage of 4.2 V until the current density reaches 0.02 mA / cm ² , and discharging is performed at 1 mA. This was performed until the battery voltage reached 2.5 V at a constant current density of / cm ² . When performing charge / discharge, based on the charge / discharge capacities of the positive electrode 31 and the negative electrode 32 obtained in advance, the negative electrode utilization rate at the first charge is set to 90%, and metallic lithium is deposited on the negative electrode 32. I tried not to. As the cycle characteristics, the capacity retention ratio at the 10th cycle with respect to the initial capacity (capacity at the 10th cycle / initial capacity) × 100 was obtained. The obtained results are shown in Tables 3-6.

As shown in Tables 3-6, according to Examples 3-1 to 35-35 and Reference Examples 3-36 to 3-39 using light metal salts having an MX bond, Comparative Example 3 not used Compared to -1 to 3-6, the capacity retention rate could be improved, and in some cases the initial capacity could also be improved. In addition, when the light metal salt having an M—X bond and LiPF ₆ were mixed and used, the initial capacity and the capacity retention rate could be further improved depending on the content. Furthermore, it was confirmed that when the content of the light metal salt having an M—X bond is 0.01 mol / kg or more and 2.0 mol / kg or less, the capacity and cycle characteristics can be improved.

That is, even when silicon which is a single metalloid element capable of forming an alloy with lithium is used as the negative electrode active material, or when the negative electrode active material layer 32B is formed by a vapor phase method, M- It was found that the capacity and cycle characteristics can be improved by including a light metal salt having an X bond. It has also been found that if the electrolyte contains a light metal salt having an MX bond and LiPF ₆ , a higher effect can be obtained by adjusting the content thereof. Furthermore, it was also found that the content of the light metal salt having an M—X bond is preferably in the range of 0.01 mol / kg to 2.0 mol / kg.

(Examples 4-1 to 4-13, Reference examples 4-14 to 4-17)
Tin is used as the negative electrode active material, and a negative electrode active material layer 32B having a thickness of 4 μm made of tin is formed by electrolytic plating on a negative electrode current collector 32A made of an electrolytic copper foil having an arithmetic average roughness Ra of 0.5 μm and a thickness of 25 μm. After that, the coin-type secondary battery shown in FIG. 3 was obtained in the same manner as in Examples 3-1 to 35-35 and Reference Examples 3-36 to 3-39 except that the negative electrode 32 was produced by heat treatment. Was made. At that time, the type and content of the light metal salt were changed as shown in Tables 7 and 8.

  Among them, Example 4-1 uses difluoro [oxolato-O, O ′] lithium borate represented by Chemical formula 10, and Examples 4-2 to 4-7 show difluoro [oxolato-O]. , O ′] lithium borate and other light metal salts are mixed and used. Example 4-8 uses tetrafluoro [oxolato-O, O ′] lithium phosphate represented by Chemical Formula 11, and Example 4-9 uses tetrafluoro [oxolato-O, O ′]. It is a mixture of lithium phosphate and other light metal salts. Example 4-10 uses lithium difluorodi [oxolato-O, O ′] lithium phosphate represented by Chemical formula 13, and Example 4-11 uses difluorodi [oxolato-O, O ′] phosphoric acid. This is a mixture of lithium and other light metal salts. In Example 4-12, tris [oxolato-O, O ′] lithium phosphate represented by Chemical formula 14 was used, and in Example 4-13, tris [oxolato-O, O ′] phosphoric acid was used. This is a mixture of lithium and other light metal salts. Reference Example 4-14 uses bis [1,2-benzenediolato (2-)-O, O ′] lithium borate represented by Chemical Formula 15, and Reference Example 4-15 is a bis [1,2-Benzenediolato (2-)-O, O ′] lithium borate and other light metal salts are used in combination. Reference Example 4-16 uses tris [1,2-benzenediolato (2-)-O, O ′] lithium phosphate represented by Chemical Formula 16, and Reference Example 4-17 includes Tris. [1,2-Benzenediolato (2-)-O, O ′] lithium phosphate and other light metal salts are used in combination.

  In Examples 4-1 to 4-13 and Reference Examples 4-14 to 4-17, when the obtained negative electrode 32 was analyzed by XPS and AES, the negative electrode active material layer 32B was found to be a negative electrode current collector 32A. It was confirmed that at least a part of the interface with the negative electrode current collector 32A was alloyed.

Further, as Comparative Examples 4-1 to 4-6 with respect to Examples 4-1 to 4-13 and Reference Examples 4-14 to 4-17, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN ( Except that only one of CF ₃ SO ₂ ) _{2 and} LiC (CF ₃ SO ₂ ) ₃ was used and the content thereof was 1.0 mol / kg with respect to the solvent, the others were as in Example 4- Secondary batteries were fabricated in the same manner as in 1-4-13 and Reference Examples 4-14 to 4-17.

  Regarding the fabricated secondary batteries of Examples 4-1 to 4-13, Reference Examples 4-14 to 4-17 and Comparative Examples 4-1 to 4-6, Examples 3-1 to 35-35, Reference Example 3 The charge / discharge test was conducted in the same manner as in −36 to 3-39, and the initial capacity and the capacity retention rate at the 10th cycle were examined. The obtained results are shown in Tables 7 and 8.

As shown in Tables 7 and 8, according to Examples 4-1 to 4-13 and Reference Examples 4-14 to 4-17 using light metal salts having an M—X bond, Comparative Example 4 not used Compared to -1 to 4-6, the capacity retention rate could be improved, and in some cases the initial capacity could also be improved. In addition, it was possible to obtain a higher effect when the light metal salt having an M—X bond and LiPF ₆ were mixed and used.

That is, it was found that even when the negative electrode active material layer 32B was formed by a liquid phase method, the capacity and cycle characteristics could be improved if the electrolyte contained a light metal salt having an MX bond. It has also been found that higher effects can be obtained if the electrolyte contains a light metal salt having an MX bond and LiPF ₆ .

(Examples 5-1 to 5-8)
A negative electrode active material layer 32B made of tin was formed by a sintering method on a negative electrode current collector 32A made of an electrolytic copper foil having an arithmetic average roughness Ra of 0.5 μm and a thickness of 25 μm, using tin as the negative electrode active material. The coin-type secondary battery shown in FIG. 3 was fabricated in the same manner as in Examples 3-1 to 35-35 and Reference Example 3-36 to 3-39 except for. Specifically, tin powder and polyvinylidene fluoride as a binder are mixed at a mass ratio of tin: polyvinylidene fluoride = 95: 5 and dispersed in N-methyl-2-pyrrolidone as a solvent. After being applied to the negative electrode current collector 32A, dried and pressurized, the negative electrode active material layer 32B was formed by firing at 200 ° C., and the negative electrode 32 was produced. The types and contents of light metal salts were changed as shown in Table 9.

  Among them, Example 5-1 uses bis [oxolato-O, O ′] lithium borate represented by Chemical Formula 12, and Examples 5-2 to 5-8 are bis [oxolato-O]. , O ′] lithium borate and other light metal salts are mixed and used.

  In addition, in Examples 5-1 to 5-8, when the obtained negative electrode 32 was analyzed by XPS and AES, the negative electrode active material layer 32B was found to have a negative electrode current collector at least at a part of the interface with the negative electrode current collector 32A. It was confirmed that it was alloyed with the electric body 32A.

In addition, as Comparative Example 5-1 with respect to Examples 5-1 to 5-8, except that LiPF ₆ was used as an electrolyte salt and the content thereof was 1.0 mol / kg with respect to the solvent, the others were carried out. Secondary batteries were fabricated in the same manner as in Examples 5-1 to 5-8.

  For the fabricated secondary batteries of Examples 5-1 to 5-8 and Comparative Example 5-1, charge / discharge tests were performed in the same manner as in Examples 3-1 to 35-35 and Reference Examples 3-36 to 3-39. The initial capacity and the capacity retention rate at the 10th cycle were examined. Table 9 shows the obtained results.

As shown in Table 9, according to Examples 5-1 to 5-8 using the light metal salt having an M—X bond, the capacity retention rate is improved as compared with Comparative Example 5-1, which is not used. In some cases, the initial capacity could be improved. In addition, it was possible to obtain a higher effect when the light metal salt having an M—X bond and LiPF ₆ were mixed and used.

That is, it was found that even when the negative electrode active material layer 32B is formed by a sintering method, the capacity and cycle characteristics can be improved if the electrolyte contains a light metal salt having an MX bond. It has also been found that higher effects can be obtained if the electrolyte contains a light metal salt having an MX bond and LiPF ₆ .

  In the above examples, the light metal salt having an M—X bond has been described with a specific example, but the above-described effects are considered to be due to the structure. Therefore, similar results can be obtained even if other light metal salts having M—X bonds are used. Moreover, although the case where the electrolytic solution is used has been described in the above embodiment, the same result can be obtained even when a gel electrolyte is used.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above embodiments and examples, a secondary battery using a gel electrolyte, which is one of an electrolytic solution or a solid electrolyte, has been described. However, the present invention provides a secondary battery using another electrolyte. The same applies to batteries. Other electrolytes include, for example, a polymer solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, an ion conductive inorganic compound made of ion conductive ceramics, ion conductive glass or ionic crystals, Or what mixed these ion conductive inorganic compounds and electrolyte solution, or what mixed these ion conductive inorganic compounds, gel-like electrolyte, or polymer solid electrolyte is mentioned.

  In the above-described embodiments and examples, a cylindrical secondary battery having a winding structure or a coin-type secondary battery has been described. However, the present invention has other structures, for example, an elliptical type having a winding structure. Alternatively, the present invention can be similarly applied to a polygonal secondary battery or a secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. Furthermore, the present invention can also be applied to a secondary battery such as a button type, a square type or a card type.

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG. It is sectional drawing showing the structure of the secondary battery formed in the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17, 36 ... Gasket, 20 ... Winding electrode body, 21 and 31 ... Positive electrode, 21A, 31A ... Positive electrode current collector, 21B, 31B ... Positive electrode active material layer, 22, 32 ... Negative electrode, 22A, 32A ... Negative electrode current collector, 22B, 32B ... Negative electrode active material layer, 23, 33 ... Separator 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead, 34 ... Exterior can, 35 ... Exterior cup.

Claims (11)

A lithium ion secondary battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer includes, as a negative electrode active material, silicon simple substance, silicon alloy, tin simple substance, tin alloy, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi. _{2, CoSi 2, NiSi 2,} CaSi 2, CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 Including at least one member selected from the group consisting of O, SiO _v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO and LiSnO;
The electrolyte includes lithium difluoro [oxolato-O, O ′] lithium borate represented by chemical formula 1, lithium tetrafluoro [oxolato-O, O ′] lithium phosphate represented by chemical formula 2, and bis represented by chemical formula 3. Lithium [oxolato-O, O ′] lithium borate, difluorodi [oxolato-O, O ′] lithium phosphate represented by chemical formula 4 and tris [oxolato-O, O ′] lithium phosphate represented by chemical formula 5 A lithium ion secondary battery comprising any one of the lithium salts.

  The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer is alloyed with the negative electrode current collector at least at a part of the interface with the negative electrode current collector.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer is formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method.   The lithium ion secondary battery according to claim 1, wherein the electrolyte further includes a solvent, and the content of the lithium salt is 0.01 mol / kg or more and 2.0 mol / kg or less with respect to the solvent. 2. The electrolyte further includes at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , a lithium salt represented by Formula ₆ and a lithium salt represented by Formula 7: Lithium ion secondary battery.

(In the formula, m and n are integers of 1 or more.)

(In the formula, p, q and r are integers of 1 or more.)   The electrolyte further includes polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, polysiloxane, Any one of the group consisting of polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene and polycarbonate, or an ion conductive inorganic compound The lithium ion secondary battery of Claim 1 containing.   The positive electrode contains a lithium-containing compound containing lithium (Li), at least one selected from the group consisting of cobalt (Co), nickel (Ni), and manganese (Mn), and oxygen (O). The lithium ion secondary battery according to 1.   The lithium ion secondary battery according to claim 1, wherein the negative electrode further contains a carbon material.   The lithium ion secondary battery according to claim 1, wherein the surface roughness of the negative electrode current collector is an arithmetic average roughness of 0.1 μm or more.   2. The lithium salt is tetrafluoro [oxolato-O, O ′] lithium phosphate represented by Chemical Formula 2 or difluorodi [oxolato-O, O ′] lithium phosphate represented by Chemical Formula 4 Lithium ion secondary battery.   2. The lithium ion secondary battery according to claim 1, wherein the negative electrode active material layer contains at least one of a simple substance of silicon, a silicon alloy, a simple substance of tin, and a tin alloy as the negative electrode active material.

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